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Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Take Away: Five Things You should be able to Explain after the DR/Adjuncts Lecture Digital Radiography – Chapter 11 Adjuncts to Radiology – Chapter 12 ¬ ¬ ¬ Brent K Stewart, PhD, DABMP Professor, Radiology and Medical Education Director, Diagnostic Physics ¬ ¬ a copy of this lecture may be found at: http://courses.washington.edu/radxphys/PhysicsCourse04http://courses.washington.edu/radxphys/PhysicsCourse04-05.html Brent K Stewart, PhD, DABMP The various types of detectors used in digital imaging (e.g., scintillators, photoconductors, etc.) The differences between the various technologies used for digital radiography (e.g., CR, indirect and direct DR) Benefits of each type (e.g., resolution, dose efficiency) Why digital image correction and processing are necessary or useful and how they are executed The various types of adjuncts to radiology (e.g., DSA or dualdual-energy imaging), what issue they are trying to resolve, mechanism exploited and end result Brent K Stewart, PhD, DABMP Digital Representation of Data (1) ¬ ¬ ¬ ¬ Digital Representation of Data (2) Bits, Bytes and Words ¬ Smallest unit of storage capacity = bit (b (binary digit digit:: or 0) Bits grouped into bytes: bits = byte Word = 16, 32 or 64 bits, depending on the computer system addressing architecture ¬ Digital Representation of Different Types of Data ¬ Storage of Positive Integers ¬ ¬ Computer storage capacity is measured in: ¬ ¬ ¬ ¬ kilobytes (kB) - 210 bytes = 1024 bytes ≈ a thousand bytes megabytes (MB) - 220 bytes = 1024 kilobytes ≈ a million bytes gigabytes (GB) - 230 bytes = 1024 megabytes ≈ a billion bytes terabytes (TB) - 240 bytes = 1024 gigabytes ≈ a trillion bytes ¬ ¬ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP Alphanumeric text, integers, and nonnon-integer data In general, n bits have 2n possible permutations and can represent integers from to 2n-1 (the range usually denoted with square brackets): n bits represents 2n values with range [0, 2n-1] bits represents 28 = 256 values with range [0, 255] 10 bits represents 210 = 1024 values with range [0, 1023] 12 bits represents 212 = 4096 values with range [0, 4095] 16 bits represents 216 = 65,536 values with range [0, 65535] Brent K Stewart, PhD, DABMP Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Conversion of Analog Data to Digital Form ¬ ¬ ¬ Digital Storage of Images The electronic measuring devices of medical scanners (e.g., transducers and detectors) produce analog signals Analog to digital conversion (analog to digital converter – ADC) ADCs characterized by ¬ ¬ ¬ ¬ sampling rate or frequency (e.g., samples/sec – MHz) number of bits output per sample (e.g., 12 bits/sample = 1212-bit ADC) ¬ Usually stored as a 2D array (matrix) of data, I(x,y): I(1,1), I(2,1), … I(n,mI(n,m-1), I(n,m) Each minute region of the image is called a pixel (picture element) represented by one value (e.g., digital value, gray level or Hounsfield unit) Typical matrices: ¬ ¬ ¬ CT: 512x512x12 bits/pixel CR: 1760x2140x10 bits/pixel DR: 2048x2560x16 bits/pixel c f Bushberg, et al., The Essential Physics of Medical Imaging, Imaging, 2nd ed., p 69 Brent K Stewart, PhD, DABMP c.f Huang, HK Elements of Digital Radiology, p Brent K Stewart, PhD, DABMP Detectors in Digital Imaging (1) ¬ ¬ ¬ ¬ Detectors in Digital Imaging (2) Gas and solidsolid-state detectors Energy deposited to ee- through Compton and photoelectric interactions Gas detectors – apply high voltage across a chamber and measuring the flow of eeproduced by ionization in the gas (typically high Z gases like Xenon: Z=54, KK-edge = 35 keV) Were used in older CT units SolidSolid-state materials ¬ SolidSolid-state detectors ¬ ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p.32 Brent K Stewart, PhD, DABMP ¬ ¬ Brent K Stewart, PhD, DABMP Electrons arranged in bands with conduction band usually empty Scintillators – some deposited energy converted to visible light Photoconductors – charge collected and measured directly Photostimulable phosphors – energy stored in electron traps c.f Yaffe MJ and Rowlands JA Phys Med Biol 42 (1997), p Elements Elements of Digital Radiology, p 10 Brent K Stewart, PhD, DABMP Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Detectors in Digital Imaging (3) Periodic Table of the Elements c.f Yaffe MJ and Rowlands JA Phys Med Biol 42 (1997), p Elements Elements of Digital Radiology, p Brent K Stewart, PhD, DABMP c.f http://www.ktfhttp://www.ktf-split.hr/periodni/en/ Computed Radiography (CR) ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Imaging plate (IP) made of PSP is exposed identically to SF radiography in Bucky IP in CR cassette taken to CR reader where the IP is separated from cassette IP is transferred across a stage with stepping motors and scanned by a laser beam (~ (~700 nm) swept across the IP by a rotating polygonal mirror Light emitted from the IP is collected by a fiberfiber-optic bundle and funneled into a photomultiplier tube (PMT) PMT converts VL into e- current c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 294 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 295 Brent K Stewart, PhD, DABMP 10 Computed Radiography (CR) System (1) Photostimulable phosphor (PSP) Barium fluorohalide: 85% BaFBr:Eu + 15% BaFI:Eu e- from Eu2+ liberated through absorption of xx-rays by PSP Liberated e- fall from the conduction band into ‘trapping sites’ near FF-centers By low energy laser light (700 nm) stimulation the e- are rere-promoted into the conduction band where some recombine with the Eu3+ ions and emit a blueblue-green (400(400500 nm) visible light (VL) Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 11 Brent K Stewart, PhD, DABMP 12 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Computed Radiography (CR) System (2) ¬ ¬ ¬ ¬ ¬ ¬ Computed Radiography (CR) System (3) Electronic signal output from PMT input to an ADC Digital output from ADC stored Raster swept out by rotating polygonal mirror and stage stepping motors produces I(t) into PMT which eventually translates into the stored DV(x,y): PMT ADC RAM IP exposed to bright light to erase any remaining trapped e- (~50%) IP mechanically reinserted into cassette ready for use 200µ 200µm and 100µ 100µm pixel size (14”x17”: 1780x2160 and 3560x4320, respectively) ¬ ¬ ¬ IP dynamic range = 104, about 100x that of SS-F (102) Very wide latitude flat contrast Image processing required: ¬ ¬ ¬ ¬ ¬ Enhance contrast SpatialSpatial-frequency filtering CR’s wide latitude and image processing capabilities produce reasonable OD or DV for either under or overexposed exams Helps in portable radiography: where the tight exposure limits of S-F are hard to achieve Underexposed quantum mottle and overexposed unnecessary patient dose c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 294 Brent K Stewart, PhD, DABMP c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 296 13 Brent K Stewart, PhD, DABMP ChargedCharged-Coupled Devices (CCD) ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Indirect Flat Panel Detectors Form images from visible light Videocams & digital cameras Each picture element (pixel) a photosensitive ‘bucket’ After exposure, the elements electronically readout via ‘shift‘shiftandand-read’ logic and digitized Light focused using lenses or fiberfiber-optics ¬ ¬ ¬ ¬ Fluoroscopy (II) Digital cineradiography (II) Digital biopsy system (phosphor screen) ¬ 1K and 2K CCDs used c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., pp 298298-299 Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 14 15 Use an intensifying screen (CsI) to generate VL photons from an xx-ray exposure Light photons absorbed by individual array photodetectors Each element of the array (pixel) consists of transistor (readout) electronics and a photodetector area The manufacture of these arrays is similar to that used in laptop screens: thinthin-film transistors (TFT) c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 301 Brent K Stewart, PhD, DABMP 16 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 ThinThin-Film Transistors (TFT) ¬ ¬ ¬ ¬ Resolution and Fill Factor After the exposure is complete and the e- have been stored in the photodetection area (capacitor), rows in the TFT are scanned, activating the transistor gates Transistor source (connected to photodetector capacitors is shunted through the drain to associated charge amplifiers Amplified signal from each pixel then digitized and stored X-ray VL e- ADC RAM ¬ ¬ ¬ ¬ ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 301 Brent K Stewart, PhD, DABMP ¬ ¬ ¬ ¬ ¬ Use a layer of photoconductive material (e.g., -Se) Se) atop a TFT array e- released in the detector layer from xx-ray interactions used to form the image directly X-ray e- TFT ADC RAM High degree of e- directionality through application of E field Photoconductive material can be made thick w/o degradation of spatial resolution Photoconductive materials ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 303 17 Direct Flat Panel Detectors ¬ Dimension of detector element largely determines spatial resolution resolution 200µ 200µm and 100µ 100µm pixel size typical For dimension of ‘a’ mm - Nyquist frequency: FN = 1/2a If a = 100µ FN = cycle/mm 100µm Fill factor = (light sensitive area)/(detector element area) TradeTrade-off between spatial resolution and contrast resolution Brent K Stewart, PhD, DABMP 18 Periodic Table of the Elements Indirect Flat Panel Detector (for comparison) Selenium (Z=34) CdTe, HgI2 and PbI2 Direct Flat Panel Detector c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 304 Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 19 c.f http://www.ktfhttp://www.ktf-split.hr/periodni/en/ Brent K Stewart, PhD, DABMP 20 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Digital versus Analog Processes & Implementation ¬ ¬ ¬ ¬ Although some of the previous image reception systems were labeled ‘digital’, the initial stage of those devices produce an analog signal that is later digitized CR: xx-rays VL PMT current voltage ADC CCD, direct & indirect digital detectors: stored e- ADC Benefits of CR ¬ ¬ ¬ ¬ Same exam process and equipment as screenscreen-film radiography Many exam rooms serviced by one reader Lower initial cost Patient Dose Considerations ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Benefits of DR ¬ Throughput : radiographs available immediately for QC & read Brent K Stewart, PhD, DABMP 21 500 450 Sep-03 Baseline Mar-04 Apr-04 S-number 350 ¬ 12 12 Photostimulable phosphors NOT include: ¬ A AnalogAnalog-toto-digital converters B Barium fluorohalide C Light detectors (blue) D Red light lasers E Video cameras ¬ Target Values ¬ Fixed Chest - [255-345] ¬ 250 200 Bone, Spine & Ext [170-230] 150 Flat panel detectors can reduce radiation dose by 22-3x as compared with CR for the same image quality due to quantum absorption efficiency & conversion efficiency 22 Huda Ch6: Digital XX-ray Imaging Question 400 300 Bone, spine and extremities: 200 Chest: 300 General imaging including abdomen and pelvis: 300/400 Brent K Stewart, PhD, DABMP Using the CR Sensitivity Number to Track Dose S-number Dashboard Main Exams Over and underexposed digital receptors produce images with reasonable OD or gray scale values As overexposure can occur, need monitoring program CR IP acts like a 200 speed SS-F system wrt QDE Use the CR sensitivity (‘S’) number to track dose ¬ 100 General Imaging incl Abdomen - [340-460] 50 MFEM MC2 MC5 MCH2 MKUB MPELV Exam Code Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 23 Brent K Stewart, PhD, DABMP 24 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Huda Ch6: Digital XX-ray Imaging Question Raphex 2002 Question: Digital Radiography ¬ 11 11 Which of the following xx-ray detector materials emits visible light: ¬ A Xenon B Mercuric iodide C Lead iodide D Selenium E Cesium iodide ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP D47 Concerning computed radiography (CR), which of the following is true? A Numerous, small solid-state detectors are used to capture the x-ray exposure patterns B It has better spatial resolution than film C It is ideal for portable x-ray examinations, when phototiming cannot be used D It is associated with high reject/repeat rates E The image capture, storage, and display are performed by the receiver 25 Brent K Stewart, PhD, DABMP Huda Ch6: Digital XX-ray Imaging Question ¬ Digital Image Correction 13 13 Photoconductors convert xx-ray energy directly into: ¬ Interpolation to fill in dead pixel and row/column defects Subtracting out average dark noise image Davg(t)(x,y) (x,y) Differences in detector element digital values for flat field ¬ Make corrections for each detector element (map) ¬ Done for DR and in a similar manner for CT (later) Not performed for CR on a pixel by pixel basis, although there are corrections on a column basis for differences in light conduction efficiency in the light guide to the PMT ¬ ¬ ¬ ¬ ¬ ¬ ¬ A Light B Current C Heat D Charge E RF energy ¬ ¬ ¬ Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 26 27 Gain image: G(x,y) G(x,y) =G’(x,y =G’(x,y)) - Davg(t)(x,y); (x,y); Gavg =(1/N) · ∑ ∑ G(x,y) I(x,y) = Gavg · [Iraw(x,y) (x,y) - Davg(t)(x,y)] (x,y)] / G(x,y) G(x,y) Brent K Stewart, PhD, DABMP 28 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Digital Image Correction Global Processing ¬ ¬ Most common global image processing: window/level Global processing algorithm ¬ ¬ ¬ ¬ ¬ ¬ ¬ I’(x,y) = c · [I(x,y) – a]: essentially y = mx + b Level (brightness) set by a Window (contrast) set by c I’ = [2 [2N/ww] /ww]·[I·[I-{wlwl-(ww/2)}], (ww/2)}], where ww = window width and wl = window level Need threshold limits when max/min [2N-1, 0] digital values encountered If I’(x,y) > Tmax I’(x,y) = Tmax If I’(x,y) < Tmin I’(x,y) = Tmin c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., pp 92 and 311 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 310 Brent K Stewart, PhD, DABMP 29 Brent K Stewart, PhD, DABMP Image Processing Based on Convolution ¬ ¬ ¬ ¬ Image Processing Based on Convolution Convolution: Ch 10 - Image Quality and Ch 13 - CT Defined mathematically as passing a NN-dimensional convolution kernel over an NNdimensional numeric array (e.g., 2D image or CT transmission profile) At each location (x, y, z, t, ) in the number array multiply the convolution kernel values by the associated values in the numeric array and sum Place the sum into a new numeric array at the same location ¬ ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 312 Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 30 31 Delta function kernel 0 0 0 0 Blurring kernel (normalization) also known as lowlow-pass filter 1/9 1/9 1/9 1/9 1/9 1/9 1/9 1/9 1/9 Edge sharpening kernel -1 -1 -1 -1 -1 -1 -1 -1 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 313 Brent K Stewart, PhD, DABMP 32 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Image Processing Based on Convolution ¬ ¬ ¬ ¬ Median and Sigma Filtering Convolution kernels can be much larger than x 3, but usually N x M with N and M odd Can also perform edge sharpening by subtracting blurred image from original highhigh-frequency detail (harmonization) The edge sharpened image can then be added back to the original image to make up for some blurring in the original image: CR unsharpmasking - freq processing The effects of convolution cannot in general be undone by a ‘dede-convolution’ convolution’ process due to the presence of noise, but a deconvolution kernel can be applied to produce an approximation: 19F MRI Brent K Stewart, PhD, DABMP ¬ ¬ ¬ ¬ ¬ 33 Multiresolution/Multiscale Processing and Adaptive Histogram Equalization (AHE) ¬ ¬ ¬ ¬ ¬ Convolution of an image with a kernel where all the values are the same, e.g (1/NxM), essentially performs an average over the kernel footprint Smoothing or noise reduction This can make the resulting output value susceptible to outliers (high or low) Median filter: rank order values in kernel footprint and take the median (middle) value Sigma filter: set sigma (σ (σ) value (e.g., 1) and throw out all values in kernel footprint > µ + σ or < µ – σ and then take the average and place in output image Brent K Stewart, PhD, DABMP 34 Unsharpmasked Spatial Frequency Processing Some CR systems (Agfa /Fuji) make use of (Agfa/Fuji) multiresolution image processing (AKA unsharpmasking) unsharpmasking) to enhance spatial resolution Wavelet or pyramidal processing on multiple frequency scales Histogram equalization rere-distributes image digital values to uniformly span the entire digital value range [2N-1,0] to maximize contrast AHE does this on a spatial subsub-region basis in an image rather than the entire image Fuji ‘Dynamic Range Control’ (DRC) a version of AHE that operates on subsub-regions of digital values c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 313 Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 35 Brent K Stewart, PhD, DABMP 36 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Histogram Equalization Properly Exposed Image Global and Adaptive Histogram Equalization OverOver-exposed Image The following images illustrate the differences between global and adaptive histogram equalization MR image with the corresponding graygray-scale histogram The histogram has a peak at minimum intensity consistent with the relatively dark nature of the image UnderUnder-exposed Image Global histogram equalization and the final graygray-scale histogram Comparing the results with the figure above we can see that the distribution was shifted towards higher values while the peak at minimum intensity remains Histogram Equalized Image c.f http://www.wavemetrics.com/products/igorpro/imageprocessing/imagetransforms/histmodification.htm http://www.wavemetrics.com/products/igorpro/imageprocessing/imagetransforms/histmodification.htm Brent K Stewart, PhD, DABMP 37 Adaptive histogram equalization shows better contrast over different parts of the image The corresponding gray-scale histogram lacks the mid-levels present in the global histogram equalization as a result of setting a high contrast level Brent K Stewart, PhD, DABMP 38 c.f http://www.wavemetrics.com/products/igorpro/imageprocessing/imagetransforms/histmodification.htm http://www.wavemetrics.com/products/igorpro/imageprocessing/imagetransforms/histmodification.htm Contrast vs Spatial Resolution in Digital Imaging ¬ ¬ ¬ ¬ Digital Imaging Systems and DQE S-F mammography can produce images w/ > 20 lp/mm According to Nyquist criterion would require 25 µm/pixel resulting in a 7,200 x 9,600 image (132 Mbytes/image) Digital systems have inferior spatial resolution However, due to wide dynamic range of digital detectors and image processing capabilities, digital systems have superior contrast resolution ¬ ¬ ¬ ¬ ¬ ¬ ¬ Remember the equation for DQE(f)? k MTF (f ) DQE(f) = [ ] -Si DR -Se DR N ⋅ NPS(f ) How can we account for this? Both CR and the screens in film/screens made thin Film higher spatial resolution than CR DQE higher for -Si systems using CsI and Gd2O2S rather than -Se (mean xx-ray E & Z) -Si DQE falling off more rapidly than -Se (geometry) c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 315 Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 39 Brent K Stewart, PhD, DABMP 40 10 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Huda Ch6: Digital XX-ray Imaging Question Huda Ch6: Digital XX-ray Imaging Question ¬ 15 15 Which of the following does NOT involve image processing: ¬ 14 14 Processing a digital xx-ray image by unsharpmask enhancement would increase the: ¬ A Background subtraction B Energy subtraction C Histogram equalization D KK-edge filtering E LowLow-pass filtering ¬ A Bit depth per pixel B Matrix size C Patient dose D Visibility of edges E Limiting spatial resolution ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP 41 Brent K Stewart, PhD, DABMP Geometric (Linear) Tomography ¬ ¬ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP Digital Tomosynthesis With the advent of CT, geometric tomography has only limited clinical utility where only one or a few planes of objects with high contrast are desired, e.g., IVP Desired slice through patient set at pivot point (focal plane) The tomographic process blurs out regions outside the focal plane, but still contributes to overall loss of contrast Larger tomographic angles result in a lessening of out of plane contributions High dose, comparable to CT for many tomographic slices c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 318 Brent K Stewart, PhD, DABMP 42 ¬ ¬ ¬ ¬ Improved version of geometric tomography where a digital detector saves an image at each of several tube angles This allows reconstruction of multiple planes through the object through shifting the various images through a certain distance before summing them Much more dose efficient, but still suffers from out of plane blurring effects Either CR or DR used c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 320 43 Brent K Stewart, PhD, DABMP 44 11 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Temporal Subtraction ¬ ¬ ¬ ¬ Digital Subtraction Angiography (DSA) – usually 1K resolution Mask (background) subtracted from images during/post contrast injection: < 1% trans visualized Motion can cause misregistration artifacts Digital value proportional to contrast concentration and vessel thickness ¬ ¬ ¬ DualDual-Energy Subtraction ¬ ¬ ¬ Is = ln(Im) – ln(Ic) = µvessel · tvessel ¬ Temporal subtraction works best when time differences between images is short Possible to spatially warp images taken over a longer period of time ¬ Exploits differences between the Z of bone (Zeff ≈ 13) and soft tissue (Zeff ≈ 7.6) Images taken either at two different kVp (two(two-shot) One image (one(one-shot) taken with energy separation provided by a filter (sandwich) Iout = loge(Ilow) – R · loge(Ihigh), where R is altered to produce softsoft-tissue predominant or bone predominant images GE Chest DR @ SCCA c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 322 Brent K Stewart, PhD, DABMP c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 324 45 Brent K Stewart, PhD, DABMP DualDual-Energy Subtraction 46 Huda Ch6: Digital XX-ray Imaging Question ¬ 22 22 The matrix size in a DSA image is typically: ¬ A 128 x 128 B 256 x 256 C 512 x 512 D 1024 x 1024 E 2048 x 2048 ¬ ¬ ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 325 Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 47 Brent K Stewart, PhD, DABMP 48 12 Digital Radiography – Bushberg Chapter 11 Adjuncts to Radiology – Bushberg Chapter 12 Diagnostic Radiology Imaging Physics Course 13 and 20 January 2005 Huda Ch6: Digital XX-ray Imaging Question Raphex 2003 Question: Digital Radiography ¬ 25 25 Changing the DSA matrix from 10242 to 20482 would NOT increase the: ¬ A Data digitization rate B Data storage requirement C Image processing time D Spatial resolution E Pixel size ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP 49 D51 A flat panel digital radiographic detector has a square 20 x 20 cm image receptor field The full field of the detector is coupled to a nominal 2048 x 2048 CCD array The relative spatial resolution (lp/mm) when going from a 20 x 20 cm to a 10 x 10 cm field of view is: A Four times better B Twice as good C The same D Half as good E One fourth as good Brent K Stewart, PhD, DABMP 50 Huda Ch6: Digital XX-ray Imaging Question ¬ 17 17 The Nyquist frequency for a 1K digital photospot image (25 cm image intensifier diameter) is: ¬ ¬ A lp/mm B lp/mm C lp/mm D lp/mm E 10 lp/mm ¬ FN (lp/mm) = 1/2a = 1/2(250mm/1024 lines) = 2.048 ≈ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP Brent K Stewart, PhD, DABMP 51 13 [...]... Huda Ch6: Digital XX-ray Imaging Question Huda Ch6: Digital XX-ray Imaging Question ¬ 15 15 Which of the following does NOT involve image processing: ¬ 14 14 Processing a digital xx-ray image by unsharpmask enhancement would increase the: ¬ A Background subtraction B Energy subtraction C Histogram equalization D KK-edge filtering E LowLow-pass filtering ¬ A Bit depth per pixel B Matrix size C Patient... Essential Physics of Medical Imaging, 2nd ed., p 324 45 Brent K Stewart, PhD, DABMP DualDual-Energy Subtraction 46 Huda Ch6: Digital XX-ray Imaging Question ¬ 22 22 The matrix size in a DSA image is typically: ¬ A 128 x 128 B 256 x 256 C 512 x 512 D 1024 x 1024 E 2048 x 2048 ¬ ¬ ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 325 Brent K Stewart, PhD, DABMP Brent K Stewart,... Huda Ch6: Digital XX-ray Imaging Question Raphex 2003 Question: Digital Radiography ¬ 25 25 Changing the DSA matrix from 10242 to 20482 would NOT increase the: ¬ A Data digitization rate B Data storage requirement C Image processing time D Spatial resolution E Pixel size ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ Brent K Stewart, PhD, DABMP 49 D51 A flat panel digital radiographic detector has a square 20 x 20 cm image receptor... receptor field The full field of the detector is coupled to a nominal 2048 x 2048 CCD array The relative spatial resolution (lp/mm) when going from a 20 x 20 cm to a 10 x 10 cm field of view is: A Four times better B Twice as good C The same D Half as good E One fourth as good Brent K Stewart, PhD, DABMP 50 Huda Ch6: Digital XX-ray Imaging Question ¬ 17 17 The Nyquist frequency for a 1K digital photospot... Subtraction ¬ ¬ ¬ Is = ln(Im) – ln(Ic) = µvessel · tvessel ¬ Temporal subtraction works best when time differences between images is short Possible to spatially warp images taken over a longer period of time ¬ Exploits differences between the Z of bone (Zeff ≈ 13) and soft tissue (Zeff ≈ 7.6) Images taken either at two different kVp (two(two-shot) One image (one(one-shot) taken with energy separation provided